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Understanding Motor Controls

Summary

Gain the knowledge that industrial electricians in the field need in order to be successful! The subject of motor controls is one of the major areas of concern for industrial electricians, and this book prepares readers for work in the industry. A "real-world" systems approach is applied to all aspects of motor control, including basic control circuits, sensing devices, solid-state controls, variable speed drives, programmable logic controllers (PLCs), and more. "Must know" applications, procedures, and operations are stressed throughout. Coverage concludes with a series of practical laboratory exercises to help provide an excellent knowledge base of important installation, testing, and troubleshooting procedures.

Table of Contents

Preface

xi

Safety Overview

1

(2)

Safety Overview

3

(1)

General Safety Rules

3

(1)

Effects of Electric Current on the Body

4

(1)

On the Job

5

(3)

Protective Clothing

8

(1)

Ladders and Scaffolds

9

(2)

Fires

11

(1)

Ground-Fault Circuit Interrupters

12

(1)

Grounding

13

(1)

Review Questions

14

(3)

Section 1 Basic Control Circuits and Components

17

(69)

General Principles of Motor Control

19

(9)

Installation of Motors and Control Equipment

19

(3)

Types of Control Systems

22

(1)

Functions of Motor Control

23

(4)

Review Questions

27

(1)

Symbols and Schematic Diagrams

28

(9)

Sensing Devices

32

(4)

Review Questions

36

(1)

Manual Starters

37

(7)

Manual Push Button Starters

40

(1)

Troubleshooting

41

(2)

Review Questions

43

(1)

Overload Relays

44

(16)

Dual Element Fuses

45

(1)

Thermal Overload Relays

45

(6)

Magnetic Overload Relays

51

(5)

Overload Contacts

56

(1)

Protecting Large Horsepower Motors

57

(2)

Review Questions

59

(1)

Relays, Contactors, and Motor Starters

60

(20)

Relays

60

(1)

Electromagnet Construction

61

(7)

Contactors

68

(4)

Mechanically Held Contactors and Relays

72

(1)

Motor Starters

73

(6)

Review Questions

79

(1)

The Control Transformer

80

(6)

Grounded and Floating Control Systems

82

(1)

Transformer Fusing

83

(2)

Review Questions

85

(1)

Section 2 Basic Control Circuits

86

(60)

Start-Stop Pushbutton Control

87

(13)

Review Questions

99

(1)

Multiple Pushbutton Stations

100

(6)

Review Questions

105

(1)

Forward-Reverse Control

106

(10)

Review Questions

111

(5)

Jogging and Inching

116

(8)

Inching Controls

120

(2)

Review Questions

122

(2)

Timing Relays

124

(9)

Pneumatic Timers

125

(1)

Clock Timers

126

(1)

Cam or Sequence Timers

127

(1)

Electronic Timers

127

(5)

Review Questions

132

(1)

Sequence Control

133

(13)

Stopping the Motors in Sequence

137

(5)

Review Questions

142

(4)

Section 3 Sensing Devices

146

(67)

Pressure Switches and Sensors

147

(6)

Differential Pressure

148

(1)

Typical Application

149

(1)

Pressure Sensors

150

(2)

Review Questions

152

(1)

Float Switches and Liquid Lever Sensors

153

(7)

Mercury Bulb Float Switch

154

(1)

The Bubbler System

155

(4)

Review Questions

159

(1)

Flow Switches

160

(4)

Review Questions

163

(1)

Limit Switches

164

(6)

Micro Limit Switches

165

(1)

Subminiature Micro Switches

166

(1)

Limit Switch Application

167

(2)

Review Questions

169

(1)

Temperature Sensing Devices

170

(10)

Expansion of Metal

170

(5)

Resistance Temperature Detectors

175

(3)

Expansion Due to Pressure

178

(1)

Review Questions

179

(1)

Hall Effect Sensors

180

(5)

Principles of Operation

180

(1)

Hall Generator Applications

181

(3)

Review Questions

184

(1)

Proximity Detectors

185

(6)

Applications

185

(1)

Metal Detectors

185

(2)

Mounting

187

(1)

Capacitive Proximity Detectors

188

(1)

Ultrasonic Proximity Detectors

188

(2)

Review Questions

190

(1)

Photodetectors

191

(10)

Applications

191

(1)

Types of Detectors

191

(5)

Mounting

196

(2)

Photodetector Application

198

(2)

Review Questions

200

(1)

Reading Large Schematic Diagrams

201

(6)

Review Questions

206

(1)

Installing Control Systems

207

(6)

Component Location

208

(1)

Point-to-Point Connection

209

(1)

Using Terminal Strips

210

(2)

Review Questions

212

(1)

Section 4 Starting And Braking Methods

213

(71)

Across-the-Line Starting

215

(5)

Alternating Current Motors

215

(2)

Direct Current Motors

217

(2)

Review Questions

219

(1)

Resistor and Reactor Starting for AC Motors

220

(7)

Resistor Starting

220

(2)

Reactor Starting

222

(1)

Step Starting

222

(4)

Review Questions

226

(1)

Autotransformer Starting

227

(6)

Open and Closed Transition Starting

230

(2)

Review Questions

232

(1)

Wye-Delta Starting

233

(11)

Wye-Delta Starting Requirements

234

(1)

Dual Voltage Connections

235

(1)

Connecting the Stator Leads

236

(2)

Closed Transition Starting

238

(2)

Overload Setting

240

(3)

Review Questions

243

(1)

Part Winding Starting

244

(6)

Overload Protection

245

(1)

Dual Voltage Motors

245

(1)

Motor Applications

246

(1)

Three Step Starting

246

(1)

Automatic ShutDown

247

(2)

Review Questions

249

(1)

Direct Current Motors

250

(12)

Field Windings

250

(1)

Armature Windings

250

(1)

Series Motors

251

(1)

Shunt Motors

252

(2)

Compound Motors

254

(1)

Field Loss Relay

254

(1)

External Shunt Field Control

254

(1)

Controlling Compounding

255

(1)

Cumulative and Differential Compounding

256

(1)

Testing the Motor for Cumulative or Differential Compounding

257

(4)

Review Questions

261

(1)

Single Phase Motors

262

(11)

Centrifugal Switch

264

(1)

Hot-Wire Starting Relay

264

(1)

Current Relay

265

(1)

Solid State Starting Relay

266

(1)

Potential Starting Relay

267

(1)

Dual Voltage Motors

268

(1)

Reversing the Direction of Rotation

269

(2)

Multispeed Motors

271

(1)

Multispeed Fan Motors

271

(1)

Review Questions

272

(1)

Braking

273

(11)

Mechanical Brakes

273

(1)

Dynamic Braking

273

(2)

Dynamic Braking for Alternating Current Motors

275

(3)

Plugging

278

(5)

Review Questions

283

(1)

Section 5 Wound Rotor, Synchronous, And Consequent Pole Motors

284

(32)

Wound Rotor Motors

285

(9)

Manual Control of a Wound Rotor Motor

287

(1)

Timed Controlled Starting

287

(1)

Wound Rotor Speed Control

288

(1)

Frequency Control

289

(3)

Review Questions

292

(2)

Synchronous Motors

294

(7)

Starting a Synchronous Motor

294

(1)

Excitation Current

295

(1)

The Brushless Exciter

295

(1)

Direct Current Generator

296

(1)

Automatic Starting for Synchronous Motors

296

(1)

The Field Contractor

296

(1)

Out-of-Step Relay

297

(1)

The Polarized Field Frequency

297

(2)

Power Factor Correction

299

(1)

Applications

300

(1)

Review Questions

300

(1)

Consequent Pole Motors

301

(15)

Three-Speed Consequent Pole Motors

304

(6)

Four-Speed Consequent Pole Motors

310

(5)

Review Questions

315

(1)

Section 6 Variable Speed Drives

316

(25)

Variable Voltage and Magnetic Clutches

317

(6)

Voltage Control Methods

317

(2)

Magnetic Clutches

319

(2)

Eddy Current Clutches

321

(1)

Review Questions

322

(1)

Solid State DC Motor Controls

323

(8)

The Shunt Field Power Supply

324

(1)

The Armature Power Supply

324

(1)

Voltage Control

325

(1)

Field Failure Control

326

(1)

Current Limit Control

327

(1)

Speed Control

327

(3)

Review Questions

330

(1)

Variable Frequency Control

331

(10)

Alternator Control

331

(1)

Solid-State Control

332

(1)

Some Related Problems

333

(1)

IGBTs

333

(2)

Advantages and Disadvantages of IGBT Drives

335

(1)

Inverter Rated Motors

335

(1)

Variable Frequency Drives Using SCRs and GTOs

336

(1)

Features of Variable Frequency Control

337

(3)

Review Questions

340

(1)

Section 7 Motor Installation

341

(20)

Motor Installation

343

(18)

Determining Motor Current

343

(4)

Determining Conductor Size for a Single Motor

347

(2)

Overload Size

349

(1)

Determining Locked-Rotor Current

350

(1)

Short-Circuit Protection

351

(1)

Starter Size

352

(3)

Example Problems

355

(1)

Multiple Motor Calculations

356

(4)

Review Questions

360

(1)

Section 8 Programmable Logic Controllers

361

(24)

Programmable Logic Controllers

363

(10)

Differences Between PLCs and PCs

363

(1)

Basic Components

364

(8)

Review Questions

372

(1)

Programming a PLC

373

(8)

Circuit Operation

374

(1)

Developing a Program

375

(2)

Converting the Program

377

(2)

Entering a Program

379

(1)

Programming Considerations

379

(1)

Review Questions

380

(1)

Analog Sensing for Programmable Logic Controllers

381

(4)

Installation

383

(1)

The Differential Amplifier

384

(1)

Review Questions

384

(1)

Section 9 Developing Control Circuits And Troubleshooting

385

(30)

Developing Control Circuits

387

(13)

Developing Control Circuits

387

(12)

Review Questions

399

(1)

Troubleshooting

400

(15)

Safety Precautions

402

(1)

Voltmeter

402

(2)

Test Procedure Example 1

404

(2)

Test Procedure Example 2

406

(8)

Review Questions

414

(1)

Section 10 Laboratory Exercises

415

(142)

Laboratory Exercises

417

(1)

Foreword

417

(1)

Parts List for Laboratory

417

(1)

Suppliers

418

(3)

Exercise 1 Basic Control

421

(11)

Review Questions

432

(14)

Exercise 2 Start-Stop Pushbutton Control

433

(13)

Review Question

446

(6)

Exercise 3 Multiple Push Button Stations

447

(5)

Review Questions

452

(10)

Exercise 4 Forward-Reverse Control

455

(7)

Review Questions

462

(10)

Exercise 5 Sequence Control

465

(7)

Review Questions

472

(12)

Exercise 6 Jogging Controls

474

(10)

Review Questions

484

(9)

Exercise 7 On-Delay Timers

487

(6)

Review Questions

493

(9)

Exercise 8 Off-Delay Timers

495

(7)

Review Questions

502

(8)

Exercise 9 Designing a Printing Press Circuit

505

(5)

Review Questions

510

(8)

Exercise 10 Sequence Starting and Stopping for Three Motors

511

(7)

Review Questions

518

(10)

Exercise 11 Hydraulic Press Control

519

(9)

Review Questions

528

(3)

Exercise 12 Design of Two Flashing Lights

529

(2)

Review Questions

531

(3)

Exercise 13 Design of Three Flashing Lights

532

(2)

Review Questions

534

(11)

Exercise 14 Control for Three Pumps

535

(10)

Review Questions

545

(5)

Exercise 15 Oil Pressure Pump Circuit for a Compressor

546

(4)

Review Questions

550

(6)

Exercise 16 Auto-Transformer Starter

552

(4)

Review Questions

556

(1)

Appendix

557

(1)

Identifying the Leads of a Three-Phase, Wye-Connected, Dual-Voltage Motor